I have two tanks of about the same size and have around 30 fish in each tank. 10-12 different mbuna species with a good mix of male and females. They are wild caughts and I should be getting some more in this weekend, 16+ to be exact and adding to my already stocked tanks. Will hopefully be able to put them into some bigger tanks soon. Presently have 3 females carrying and nets with 3-4 sets of fry hanging on the sides of these tanks. No problems experienced with serious aggression at all. In amounsgt this all I also have young fry swimming in the tanks. A true reflection of what the Lake condition, regarding fish numbers, is.
I would look to re-arranging your rocks to create a better cave set up. This is vital for the existence of these fish. I initially had my rocks running the length of the tank but then changed to a pile at each end. This put a stop to 1 more dominant male trying to control the entire reef. Their territory in the Lkae might extend to uo to 10ft around their nest, so the tank situation is small in comparison.
The species you have tend to be less aggressive than some of the others available. Look at putting in a sand fine coral grit mix as it seems as though they like to sift through this, especially after being fed. I had gravel initially in my one tank but found the sand easier to keep. Do regular weekly 20% water changes and you should not have too many problems.
Just remeber when you want to add new fish try to add at least 3-4 fish at a time. Adding in a single fish will almost certainly spell disaster for it.
Remember you get everybodies personal experience, all good, when you ask for advice. You need to sum it up and then try and see what works best for you.
Good luck with your endeavour.
